1. Field of the Invention
This invention relates to an elevated temperature pressure swing adsorption system for separation of feed gas mixtures, to yield product gases such as oxygen, nitrogen, inert gas, etc.
2. Description of the Related Art
In the field of gas separation for the production of industrial gases, a variety of technologies have been employed in the art, including: cryogenic separation processes involving cooling and pressurizing a feed gas mixture to form a liquid that then undergoes distillation; chemisorption or chemical reaction removal of unwanted gas species from a feed gas mixture to yield the desired gas component as the only remaining gas-phase product; scrubbing of the feed gas mixture to remove undesired soluble components therefrom, chromatographic separation of the feed gas mixture; and physical adsorption-based processes.
The latter approach of physical adsorption-based processes includes pressure swing adsorption (PSA) in which a bed of physical adsorbent material is contacted with a feed gas mixture including one or more components for which the physical adsorbent material has sorptive affinity, to preferentially adsorb such components, while the non-adsorbed components flow out of the contacting zone containing the adsorbent material. The adsorbent material then is lowered in pressure in relation to the pressure at which the feed gas mixture is contacted with the adsorbent material, e.g., by a xe2x80x9cblow-downxe2x80x9d or depressurization step, or alternatively by vacuum desorption, whereby the previously sorbed gas components desorb from the adsorbent material and are discharged from the adsorbent material.
The foregoing PSA process may be carried out in a multiplicity of adsorbent beds, joined together by valved manifolds at their respective inlet ends and at their outlet ends, and coupled at the inlet manifold to a source of the feed gas mixture to be separated. In operation, the valves are operated to carry out a cyclic, repetitive process in which at least one of the beds is undergoing active processing of gas mixture, while another or others are off-line or undergoing regeneration. Thus, a first bed of a multibed PSA system may be undergoing pressurization with feed gas mixture, while a second bed undergoes depressurization and discharge of previously sorbed gas therefrom. The regeneration may entail use of a purge or displacement gas, or use of embedded heat exchange coils to aid in desorbing gas from the bed.
A wide variety of sorbent materials have been used or proposed for use in PSA systems, including zeolites, activated carbon, silica, alumina, etc. The search for new sorbent materials forms a continuing focus of the gas products industry, particularly for the production of commodity industrial gases such as oxygen, nitrogen, argon, etc.
By way of specific example, systems for the commercial production of oxygen from air by PSA or vacuum-pressure swing adsorption (VPSA) frequently use zeolites as an adsorbent. Nitrogen is more strongly adsorbed than oxygen on zeolites, so when high pressure air is placed in contact with these materials, an oxygen-rich atmosphere is left. Lowering the pressure over the adsorbent bed allows the adsorbed nitrogen to reenter the gas phase (such desorbate then may be used as a nitrogen source), and the cycle is repeated. Using vacuum in the cycle (PVSA) results in slightly better performance.
PSA and VPSA techniques alone typically deliver oxygen with a purity of 90-95%, with nitrogen and argon as the major impurities. Where this purity level is acceptable, oxygen can be generated on-site.
Oxygen, however, frequently is desired to be produced at a purity level on the order of 99+%, and this is difficult to achieve economically in commercially available PSA and VPSA systems.
Polymeric membrane processes have been suggested as a potential solution to this problem, in view of the conceptually low capital costs, small size, light weight and simple operation of membrane-based separation systems. Nonetheless, efforts to produce oxygen economically with polymeric membranes have not been successful, as a result of poor permeation selectivity in commercially available polymeric membranes. In consequence, current polymeric membrane systems are not available to produce oxygen in high purity. Single-pass membrane units deliver 35-40% oxygen. Multiple pass units can go over 90%, but are not able to economically reach the aforementioned high purity threshold of 99+%.
The present invention provides a PSA system that economically and efficiently sorptively removes oxygen from an oxygen-containing feed gas mixture, and is capable of producing extremely high levels of purity of product gas due to the high selectivity of the adsorbent of the present invention for oxygen.
In one aspect, the invention relates to a pressure swing adsorption system for processing an oxygen-containing feed gas mixture to extract oxygen therefrom, comprising an adsorbent bed arranged for elevated temperature sorption/desorption operation, wherein the adsorbent bed comprises a ceramic adsorbent having affinity for oxygen when the ceramic adsorbent is at elevated temperature, e.g., from about 400 to about 1000xc2x0 C., and more preferably in the range of from about 600 to about 900xc2x0 C.
The ceramic adsorbent may comprise a material such as:
oxide fluorite oxygen ion conductors of the formula A4O8;
pyrochlore material of the formula A2B2O7;
material of the formula Bi2O3(A2O6);
stabilized forms of d-Bi2O3;
Y2O3 and/or ZrO2 stabilized d-Bi2O3;
Bi24Pb5Ca3O44;
Bi14V2O11;
perovskite materials of the formula ABO3;
oxide Brown Millerite electrolytes of the formula A2B2O5;
mixed Brown Millerite electrolytes of the formula ABO3ABO2.5;
A4O6ABO2.5 compositions;
mixed superconducting (ABO3AO) electrolytes;
cryolite (A3BO3) electrolytes;
columbite (AB2O6) electrolytes;
and corresponding doped materials,
wherein A and B are metals independently selected from the group consisting of lanthanum, aluminum, strontium, titanium, calcium, zirconium, iron, barium, indium, gadolinium, yttrium, copper, cerium, thorium, bismuth, cobalt, nickel, magnesium, manganese, vanadium, chromium, niobium, tantalum, boron, hafnium, neodymium, terbium, ytterbium, erbium, thullium, lutetium, samarium, lead, tin, lawrencium, and praseodymium.
In another aspect, the invention relates to a pressure swing adsorption system comprising:
an adsorbent vessel containing a ceramic adsorbent having sorptive affinity for oxygen when the ceramic adsorbent is heated to elevated temperature in a range of from about 400xc2x0 C. to about 1000xc2x0 C.;
a source of an oxygen-containing feed gas mixture arranged to selectively flow the oxygen-containing feed gas mixture into the adsorbent vessel for contact with the ceramic adsorbent therein at higher pressure to remove at least part of the oxygen from the oxygen-containing feed gas mixture and yield an oxygen-depleted gas;
a heat source arranged to heat the ceramic adsorbent in the adsorbent vessel to elevated temperature in the aforementioned range of from about 400xc2x0 C. to about 1000xc2x0 C.;
such adsorbent vessel being arranged to discharge oxygen-depleted gas from the vessel at lower pressure;
a motive fluid driver coupled to the adsorbent vessel and arranged for selective actuation thereof to impose said lower pressure on the ceramic adsorbent so that oxygen removed from the oxygen-containing feed gas mixture by the ceramic adsorbent is released from the ceramic adsorbent under said lower pressure and discharged from the bed.
A further aspect of the invention relates to a pressure swing adsorption system comprising at least one adsorbent vessel arranged for higher pressure adsorption and lower pressure desorption in a cyclic alternating and repeating sequence of steps, each adsorbent vessel containing a bed of a ceramic adsorbent having a sorptive affinity for oxygen when the adsorbent is at elevated temperature, a source of oxygen-containing feed gas mixture arranged for introduction of the feed gas mixture to each adsorbent vessel of the system in sequence as a feed step for said higher pressure adsorption in said cyclic alternating and repeating sequence of steps, a heater arranged to maintain the adsorbent in each adsorbent vessel at elevated temperature, and a pump arranged to withdraw oxygen-enriched gas from each adsorbent vessel in sequence after the feed step, as a recovery step for said lower pressure desorption in said cyclic alternating and repeating sequence of steps, and a cycle time controller arranged to effect the feed step and recovery step in alternating sequence to one another in each adsorbent bed.
A still further aspect of the invention relates to a method for processing an oxygen-containing feed gas mixture to extract oxygen therefrom, comprising contacting the oxygen-containing feed gas mixture with a ceramic adsorbent having affinity for oxygen, under process conditions effective for extracting oxygen from the feed gas mixture.
Another aspect of the invention relates to a method for the extraction of oxygen from an oxygen-containing feed gas mixture, by contacting such feed gas mixture with a ceramic sorbent material having sorptive affinity for oxygen at elevated temperature, wherein such contacting is carried out in a PSA system at elevated temperature in the range of 400xc2x0 C.-1000xc2x0 C.
Other objects, features and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.